In high average power diode pumped solid state lasers, large diode laser pump arrays are commonly used to pump large aperture amplifiers. Developments in diode laser pumps have resulted in high output powers suitable for pumping high power solid state lasers. As a result, diode laser pumps have replaced flash lamp pumps in many applications.
FIG. 1 is a simplified perspective illustration of a two-dimensional array of diode lasers (i.e., semiconductor lasers). The diode laser array 100 includes a number of diode laser bars 110 stacked together with heat exchangers 120 on a base 130. The heat exchangers 120 may be actively cooled micro-channel heat exchangers or the like. Heat conductors 140a and 140b may be utilized to provide an additional thermal path for removal of heat generated by the laser diode bars 110. Each individual laser bar includes a horizontally disposed array of lasers 112, each emitting pump radiation. Thus, the diode laser array 100 includes M×N lasers, where M is the number of diode laser bars 110 and N is the number of lasers 112 per bar.
Although diode pumping offers dramatically increased efficiency, longevity, and decreased heat loading relative to flash lamp pumping, diode laser pump arrays typically provide anisotropic (uneven) illumination. As illustrated in FIG. 2, because of the generally oval shape of the beam at the laser facet, the divergence of an output beam from a diode laser is anisotropic, with the divergence angle in the vertical plane (θV) being significantly greater than the divergence angle in the horizontal direction (θH). Lenslet arrays mounted in front of the diode laser bars, with a horizontally disposed lenslet array matched to each horizontal laser bar, have been used to decrease the divergence angle in the vertical plane to a value approximately equal to the divergence angle in the horizontal direction.
Despite the matching of divergence angles using lenslet arrays, there is a need in the art for improved methods and systems for homogenizing the beams of diode laser pump arrays.